The present invention relates to fiber-optic communications networks, and more particularly, to optical communications links based on equipment such as optical amplifiers having double-pass arrangements in which optical signals traverse the same components in each of two passes.
Fiber-optic networks are used to support voice and data communications. In optical networks that use wavelength division multiplexing, multiple wavelengths of light are used to support multiple communications channels on a single fiber.
Optical amplifiers are used in fiber-optic networks to amplify optical signals. For example, optical amplifiers may be used to amplify optical data signals that have been subject to attenuation over fiber-optic paths. A typical amplifier may include erbium-doped fiber coils that are pumped with diode lasers. Raman amplifiers have also been investigated. Discrete Raman amplifiers may use coils of dispersion-compensating fiber to provide Raman gain. Distributed Raman amplifiers provide gain in the transmission fiber spans that are used to carry optical data signals between network nodes.
It is an object of the present invention to provide improved optical network equipment such as optical amplifiers.
It is also an object of the present invention to provide optical network equipment such as optical amplifiers based on double-pass configurations in which the optical data signals being handled by the equipment travel forwards and backwards through at least some of the same components in the equipment.
These and other objects of the invention are accomplished in accordance with the present invention by providing optical amplifiers and other optical network equipment having optical gain stages for use in fiber-optic communications links in fiber-optic networks. The fiber-optic links may be used to carry optical data signals associated with wavelength-division-multiplexing channels.
The equipment may be based on a double-pass configuration. With this arrangement, at least part of the optical path through the equipment involves a region of optical components through which the optical data signals travel in both forward and backward directions. A reflector at one end of the path may be used to reflect forward-propagating optical data signals in the backwards direction.
Various components may be included in the double-pass region of the equipment. For example, gain stages, optical modules such as dispersion compensation modules, static and dynamic spectral filters, variable optical attenuators, and other components may be included in the double-pass path.